1. Field of the Invention
The present invention relates to an optical deflector comprising an optical waveguide having a deflection mechanism for use in optical communication, measurement, information processing, etc., and a process for producing the same.
2. Description of the Prior Art
Optical waveguides having such a deflection mechanism include a planar optical waveguide and a fiber optical waveguide. When the term "optical waveguide" is simply mentioned in the following description of the present invention, it is intended to encompass both of a planar optical waveguide and a fiber optical waveguide. In other cases where specific mention is necessary, one type is referred to as a "planar optical waveguide", while other type is referred to as a "fiber optical waveguide" or an "optical fiber."
A 45-degree oblique end face mirror, formed by providing a planar optical waveguide or a fiber optical waveguide with a 45-degree oblique end face, is capable of compact 90-degree deflection. Accordingly, an optical deflector comprising a planar optical waveguide provided with the above-mentioned mirror and an optical deflector comprising a fiber optical waveguide provided with the above-mentioned mirror are expected to be elements effective, for example, in providing a high level of integration of an optical module and reducing the assembling cost.
Active study and development have particularly recently been made of optical transmitter and receiver with a structure wherein arrayed surface emitting (surface sensitive) optical devices are coupled with optical waveguides disposed in horizontal directions relative to the emitting (sensitive) surface of these surface emitting (sensitive) optical devices by means of 45-degree oblique end face mirrors formed at ends of the optical waveguides in order to produce compact and inexpensive parallel optical transmitter and receiver.
Reported technologies of forming a 45-degree oblique end face mirror at an end of a planar optical waveguide include (1) a method wherein an end portion thereof is mechanically cut off obliquely with a microtome (see B. L. Booth, "Polymers for integrated optical waveguides," in Polymers for Electronic and Photonic Applications, C. P. Wong, Ed., New York: Academic, 1993, pp. 549-599), (2) a method wherein such an oblique end face mirror is formed by reactive ion etching [see H. Takahara et al, Proc. of SPIE, vol. 1849, 70-78 (1993)], (3) a laser abrasion method, and (4) a method wherein a 45-degree cut is made with a thin rotary blade [see Osamu Mikami et al, "Hikari Jisso Gijutu no Tenbo (A Review of Optical Packaging Technology)," Shingaku Giho (Shingaku Bulletin), OPE95-47 (1995-08)].
FIGS. 1 and 2 are diagrams illustrating the method (1) wherein an end portion of a planar optical waveguide is mechanically cut off obliquely with a microtome. In FIGS. 1 and 2, numeral 201 refers to a waveguide film, 202 to a blade, 203 to waveguide films having respective oblique end face mirrors formed at the ends thereof by cutting-off with the blade 202. According to the method shown in FIGS. 1 and 2, the waveguide film 201 fixed oblique by 45 degrees relative to the cut-off direction is cut off with the blade 202 to form oblique micro-mirrors (face mirrors). This method (1) is simple but involves problems such as (1-i) an inapplicability thereof to an optical waveguide formed from a rigid material such as glass and to an optical waveguide supported on a rigid substrate such as a silicon or glass substrate, (1-ii) an incapability of forming oblique end face mirrors only for some of optical waveguides formed in parallel with each other in one and the same sample, though possible for all of the optical waveguides, (1-iii) a difficulty in highly accurately positioning a location where an oblique end face mirror is formed, and (1-iv) a slight increase in reflection loss because of a limited smoothness of cut-off surfaces.
On the other hand, the method (2) wherein an oblique end face mirror is formed by reactive ion etching involves problems such as (2-i) a complicated and time-consuming step, (2-ii) a difficulty in determining etching conditions and a difficulty in forming an oblique end face mirror with a good accuracy of the angle of inclination thereof.
On the other hand, the laser abrasion method (3) involves problems such as (3-i) expensive equipment and time-consuming mirror formation, and (3-ii) a difficulty in determining etching conditions and a necessity of great alterations in mirror formation equipment and conditions for every material.
FIGS. 3 and 4 are diagrams illustrating the method (4) wherein a 45-degree cut in a planar optical waveguide is made with a rotary blade to form oblique end face mirrors. In FIGS. 3 and 4, numeral 204 refers to a substrate, 205 to a lower cladding layer, 206 to a core, 207 to an upper cladding layer, 208 to a rotary blade, and 209 to a 45-degree cut. According to this method, a sample is fixed to have the optical axis of the planar optical waveguide at an angle of 45 degrees with the rotary blade, and then cut with the rotary blade 208 at an angle of 45 degrees to form the 45-degree cut 209 in a waveguide consisting of a core and a cladding. This method (4), though advantageous in that a mirror plane excellent in smoothness can be formed by selecting a suitable blade, involves problems such as, (4-i) such a difficulty in fixing a sample as to require specially devised equipment, (4-ii) a difficulty in controlling the angle, and (4-iii) a difficulty in smoothing the oblique end faces by secondary working or processing because the oblique end faces are formed in a narrow cut groove.
On the other hand, a method (5) wherein an end face of an optical fiber is polished obliquely using a polishing machine [see K. P. Jackson et al., Proc. of SPIE, vol. 994, 40-47 (1988)] was contrived as a technology of forming a 45-degree oblique end face mirror at an end of an optical fiber. This method, though widely used due to its capability of obtaining a smooth optical mirror plane, involves problems such as (5-i) a difficulty in securing an accuracy of a position where an oblique end face mirror is formed, (5-ii) a difficulty in delicately controlling the angle of inclination of a mirror plane, (5-iii) a difficulty in polishing a number of samples at once and a low productivity because of the necessity of a long polishing time, and (5-iv) a methodological incapability of localized mirror formation midway of optical paths of a fiber sheet or a fiber board having optical fibers embedded in the sheet or board with a resin.
Meanwhile, in a surface emitting laser for ordinary use in an optical transmitter and receiver module designed to be inexpensive, an oscillation wavelength is in a 0.85 .mu.m band. Thus, it is important that a waveguide material involves a low loss in this wavelength band. For example, a polyimide known as a heat-resistant polymeric material involves an electron transition absorption ranging from the ultraviolet region to the visible light region with a high loss of about 1 dB/cm in the 0.85 .mu.m band. Accordingly, an optical waveguide made of a conventional material is unsuitable for use as an optical waveguide constituting an optical deflector.
As described above, conventional optical deflectors comprising an optical path of a planar optical waveguide type are problematic in respect of the method of forming an oblique end face mirror. Specifically, the method (1) wherein oblique end face mirrors are formed by a cutting-off operation involves problems such as (1-i) an inapplicability thereof to an optical waveguide formed using a rigid material or supported on a rigid substrate, (1-ii) an incapability of forming oblique end face mirrors only for some of optical waveguides formed in parallel with each other in one and the same sample, (1-iii) a difficulty in securing an accuracy of a position where oblique end face mirrors are formed, and (1-iv) a slightly high reflection loss attributed to the roughness of cut-off surfaces.
On the other hand, the method (2) wherein an oblique end face mirror is formed by reactive ion etching involves problems such as (2-i) a complicated and time-consuming step, (2-ii) a difficulty in determining conditions and a difficulty in putting the angle of inclination of an oblique end face mirror in accurate agreement with the desired angle.
On the other hand, the laser abrasion method (3) involves problems such as (3-i) expensive equipment and time-consuming mirror formation, and (3-ii) a difficulty in determining etching conditions and a necessity of great alterations in mirror formation equipment arid conditions for every material.
On the other hand, the method (4) wherein a 45-degree cut in a planar optical waveguide is made with a rotary blade to form oblique end face mirrors involves problems such as, (4-i) such a difficulty in fixing a sample as to require specially devised equipment, (4-ii) a difficulty in controlling the angle, and (4-iii) a difficulty in smoothing the oblique end faces by secondary working or processing because the oblique end faces are formed in a narrow cut groove.
On the other hand, in a conventional optical deflector comprising an optical fiber type, an oblique end face mirror is formed by oblique polishing, but the oblique polishing method (5) involves problems such as (5-i) a difficulty in securing an accuracy of a position where an oblique end face mirror is formed, (5-ii) a difficulty in delicately controlling the angle of inclination of a mirror plane, (5-iii) a difficulty in polishing a number of samples at once and a low productivity because of the necessity of a long polishing time, and (5-iv) a methodological incapability of localized mirror formation midway of optical paths of a fiber sheet or a fiber board having optical fibers embedded in the sheet or board with a resin.